In recent years research has focused on the use of starch as an industrial raw material, which can reduce dependence on non-renewable resources. It is recognized that starch is composed of two components, a linear amylose component and a branched amylopectin component. Starches from different sources, for example, potato, corn, tapioca, and rice, are characterized by different relative proportions of the amylose and amylopectin components, which influence physicochemical properties such as gelatinization, water absorption and melt viscosity [Determination of Amylose Content in Different Starches Using Modulated Differential Scanning calorimetry, Moorthy, S. N., et al, Starch, 58 (2006) 209-214]. Several processes have been developed to produce a starch high in either amylose or amylopectin, including physical means of separation, classical plant breeding, and genetically engineered modification of the plants, such that primarily one type of starch is produced.
Generally, the physical properties of products comprising starch will improve when the amylose content is high. However, high amylose starches are more expensive than ‘natural’ low amylose starches (sometimes referred to as commodity starches) often leading to a trade off between price and performance.
Native starches may also be modified, via chemical, biochemical, and/or physical means, in order to produce certain properties. For example, chemical modification processes such as etherification or esterification retard starch retrogradation and effectively plasticise the starch, making it behave like a thermoplastic.
Although the efficacy of these special and modified starches is recognized, their cost may inhibit commercial acceptability of the products made from them. Furthermore, replacement of, for example, high amylose starch with a proportion of commodity low amylose starch, although providing starch compositions of overall lower cost, may also adversely affect physical properties.
Therefore a need remains to provide starch compositions that have desirable physical properties and which utilise inexpensive, renewable materials.